1. Field of the Invention
The present invention relates to a manufacturing method of nitride semiconductor light emitting elements.
2. Description of the Related Art
A transparent substrate made of sapphire is usually used as a growth substrate for film formation for nitride semiconductor light emitting elements, and a plurality of nitride semiconductor light emitting elements are formed by film formation on a surface of the sapphire substrate.
Because the heat conductivity of sapphire is as low as 20 W/mK, in order to obtain good heat radiation, the nitride semiconductor side needs to be stuck to a heat sink, a sub-mount, or the like. In this case, light is extracted from the sapphire substrate side, but a lot of light is reflected at the sapphire substrate back surface, resulting in a reduction in light extraction efficiency. Accordingly, a technique has been taken where after another support substrate including, e.g., a package substrate of high heat conductivity is stuck to the nitride semiconductor side, the sapphire substrate is removed by laser lift-off.
When sticking it to another support substrate, the problem occurs that if flat surfaces of large area are stuck together, atmospheric gas or the like is caught between the stuck-together surfaces, resulting in the occurrence of voids.
Further, in the laser lift-off, for example, light having a wavelength shorter than the wavelength 362 nm of the absorption edge of GaN (gallium nitride) is projected from the back side of the sapphire substrate so as to decompose GaN adjacent to the interface with the sapphire substrate into gallium and nitrogen, thereby separating the sapphire substrate. However, where the flat surfaces of large area are stuck together, nitrogen gas occurring in the laser lift-off is less likely to escape to the surrounding area and stays in situ, thus causing another problem that a large impact occurs on the GaN film.
Hence, a technique is carried out where after the nitride semiconductor on the sapphire substrate is divided into individual light emitting elements, the resultant is stuck to another support substrate and where the sapphire substrate is removed by laser lift-off.
In the case of a group-III nitride semiconductor, because its crystal is chemically stable, it is very difficult to wet etch it, and dry etching is used for processing its shape. However, the processed shape in dry etching is usually a forward tapered shape, and hence if a nitride semiconductor is divided into individual elements and then stuck to another support substrate as in the above technique, the side walls of the elements will have an inverse tapered shape.
Hence, it is difficult to form a feeder line leading to the surface (usually an n-type GaN surface) from which the sapphire substrate is removed, on those side walls.
Accordingly, there are a technique in which feeder lines are provided by wire-bonding and a technique in which with a flip-chip structure (where an n-electrode and a p-electrode are arranged on the same side) being used for the electrode structure, it is aligned with a package substrate having a feeder line pattern formed beforehand so as to stick them together. Refer to Japanese Patent Kokai No. 2006-128710 (Patent Literature 1).